Bragg grating, and spectroscopy device including the bragg grating

ABSTRACT

Provided are a Bragg grating and a spectroscopy device including the same. The Bragg grating is disposed at each of opposite ends of a resonator for reflecting light of a certain wavelength band and includes a core member extending from a waveguide of the resonator in a lengthwise direction of the waveguide; a plurality of first refractive members protruding from the core member and spaced apart from each other along the lengthwise direction; and a second refractive member filling spaces between the first refractive members and having a refractive index different from a refractive index of the first refractive members.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional application of U.S. application Ser. No. 15/208,953filed on Jul. 13, 2016, which claims priority from Korean PatentApplication No. 10-2015-0166416, filed on Nov. 26, 2015 in the KoreanIntellectual Property Office, the disclosures of which are incorporatedherein by reference in their entirety.

BACKGROUND 1. Field

Apparatuses and methods consistent with exemplary embodiments relate toBragg gratings and spectroscopy devices including the Bragg gratings.

2. Description of the Related Art

Biometric technology on wearable devices allows users to measurebiometric information such as blood glucose in a non-invasive manner.When the wearable devices are implemented with a spectrometer, the sizeof the spectrometer may have to be ultra-small to fit in the wearabledevices. . By implementing Fabry-Pero interferometers having differentlengths as a chip by using silicon (Si)-photonics technology, anultra-small size spectrometer may be manufactured. A Fabry-Perotinterferometer includes a resonator and Bragg gratings at opposite endportions of the resonator. An important factor is to manufacture a Bragggrating having high reflectivity on the desired wavelength range of awearable device.

SUMMARY

One or more exemplary embodiments provide Bragg gratings andspectroscopy devices including the Bragg gratings.

According to an aspect of an exemplary embodiment, there is provided agrating disposed at each of opposite ends of a resonator for reflectinglight of a certain wavelength band including: a core member extendingfrom a waveguide of the resonator in a lengthwise direction of thewaveguide; a plurality of first refractive members protruding from thecore member and spaced apart from each other along the lengthwisedirection; and a second refractive member filling spaces between thefirst refractive members and having a refractive index different from arefractive index of the first refractive members.

The first refractive members may protrude from opposite sides of thecore member in a width direction of the core member. At least some ofpitches between the first refractive members may vary along thelengthwise direction.

At least one of a width of the core member and protruding lengths of thefirst refractive members may vary along the lengthwise direction. Thewidth of the core member may gradually reduce toward a center portion ofthe core member along the lengthwise direction. The protruding lengthsof the first refractive members may gradually increase toward the centerportion of the core member along the lengthwise direction.

The first refractive members may face each other across on the coremember. The width of the core member may be less than a width of thewaveguide in the resonator.

Each of the core member and the first refractive members may includesilicon nitride. The second refractive member may include silicon oxide.

According to an aspect of another exemplary embodiment, there isprovided a grating disposed at each of opposite ends of a resonator forreflecting light of a certain wavelength band including: a core memberextending from a waveguide of the resonator in a lengthwise direction ofthe waveguide; a plurality of first refractive members protruding fromthe core member; and a second refractive member filling spaces betweenthe first refractive members, wherein pitches between the plurality offirst refractive members may vary along the lengthwise direction, andwherein at least one of a width of the core member and protrudinglengths of the first refractive members may vary along the lengthwisedirection.

The plurality of first refractive members may protrude from oppositesides of the core member in a width direction of the core member.

A width of the core member may gradually reduce along the lengthwisedirection of the core member toward a center portion of the core member,and protruding lengths of the plurality of first refractive members maygradually increase along the lengthwise direction toward the centerportion of the core member.

According to an aspect of an exemplary embodiment, there is provided aspectrometer including: a resonator; and a grating disposed at each ofopposite ends of the resonator and configured to reflect light of acertain wavelength band, wherein the grating may include: a core memberextending from a waveguide of the resonator in a lengthwise direction ofthe waveguide; a plurality of first refractive members protruding fromthe core member and spaced apart from each other along the lengthwisedirection; and a second refractive member filling spaces between theplurality of first refractive members.

The plurality of first refractive members may protrude from oppositesides of the core member in a width direction of the core member. Atleast some of pitches between the first refractive members may varyalong the lengthwise direction.

At least one of a width of the core member and protruding lengths of thefirst refractive members may vary along the lengthwise direction. Thewidth of the core member may gradually reduce toward a center portion ofthe core member along the lengthwise direction, and protruding lengthsof the first refractive members may gradually increase toward the centerportion of the core member along the lengthwise direction.

The second refractive member may cover the waveguide of the resonator,the core member, and the plurality of first refractive members. Thespectroscopy units may be on a silicon substrate.

According to an aspect of another exemplary embodiment, there isprovided a spectrometer including: a resonator that extends to an endpoint on a longitudinal axis; and a reflector disposed at the end pointof the resonator, the reflector including a core member extendingoutwardly from the end point of the resonator on the longitudinal axis,and a plurality of pairs of arms extending from the core member to beperpendicular to the core member, wherein the plurality of pairs of armsare spaced apart from each other on the longitudinal axis by aninterval.

The interval may decrease toward a center point of the core member onthe longitudinal axis.

A span of the plurality of arms may increase toward a center point ofthe core member on the longitudinal axis.

A pair among the plurality of pairs of arms may include a first arm anda second arm. The first arm may extend from the core member in a firstdirection, the second arm may extend from the core member in a seconddirection opposite to the first direction, and the first arm and thesecond arm may be disposed at a same position of the core member on thelongitudinal axis.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects will be more apparent by describingcertain exemplary embodiments, with reference to the accompanyingdrawings in which:

FIG. 1 is a perspective view of a Fabry-Perot interferometer having ageneral structure;

FIG. 2 is a cross-sectional view of the Fabry-Perot interferometer ofFIG. 1;

FIG. 3 is a perspective view of a Bragg grating shown in FIG. 1;

FIG. 4 is a diagram showing reflectivity of the Bragg grating of FIG. 3;

FIG. 5 is a plan view of a spectroscopy device according to an exemplaryembodiment;

FIG. 6 is a perspective view of a spectroscopy unit shown in FIG. 5;

FIG. 7 is an internal plan view of a Bragg grating shown in FIG. 6;

FIG. 8 is a diagram showing reflectivity of the Bragg grating of FIG. 7;

FIG. 9 is an internal plan view of a Bragg grating according to anotherexemplary embodiment;

FIG. 10 is a graph of a reflectivity of the Bragg grating of FIG. 7 withrespect to reflectivity of the Bragg grating of FIG. 9;

FIG. 11 is an internal plan view of a Bragg grating according to anotherexemplary embodiment;

FIG. 12 is a graph of reflectivity of the Bragg grating of FIG. 9 withrespect to reflectivity of the Bragg grating of FIG. 11; and

FIG. 13 is a graph of reflectivity of the Bragg grating of FIG. 4 withrespect to reflectivity of the Bragg grating of FIG. 11.

DETAILED DESCRIPTION

Exemplary embodiments are described in greater detail below withreference to the accompanying drawings.

In the following description, like drawing reference numerals are usedfor like elements, even in different drawings. The matters defined inthe description, such as detailed construction and elements, areprovided to assist in a comprehensive understanding of the exemplaryembodiments. However, it is apparent that the exemplary embodiments canbe practiced without those specifically defined matters. Also,well-known functions or constructions are not described in detail sincethey would obscure the description with unnecessary detail.

It will be understood that when a component, such as a layer, a film, aregion, or a plate, is referred to as being “on” another component, thecomponent may be directly on the other component or interveningcomponents may be present thereon. In addition, materials forming eachlayer in exemplary embodiments are examples, and thus, other materialsthan the examples below may be used. As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items. Expressions such as “at least one of,” when preceding alist of elements, modify the entire list of elements and do not modifythe individual elements of the list.

FIG. 1 is a perspective view of a Fabry-Perot interferometer 100 havinga general structure, FIG. 2 is a cross-sectional view of the Fabry-Perotinterferometer 100 of FIG. 1, and FIG. 3 is a perspective view of aBragg grating 120 shown in FIG. 1.

Referring to FIGS. 1 to 3, the Fabry-Perot interferometer 100 mayinclude a resonator 110 having a waveguide 111 of a predeterminedlength, and Bragg gratings 120 at opposite ends of the resonator 110.The waveguide 111 of the resonator 110 may include, for example, siliconnitride.

The Bragg grating 120 may reflect light of a predetermined wavelengthband. The Bragg grating 120 may include a plurality of first refractivemembers 121 arranged in a lengthwise direction (e.g., x-direction inFIG. 1) of the resonator 110, and a second refractive member 122 fillingspaces between the first refractive members 121. A width W of the Bragggrating 120 in a y-direction may be equal to a width D of the waveguide111 in the y-direction of the resonator 110.

The first refractive members 121 may have a refractive index differentfrom a refractive index of the second refractive member 122. Forexample, the first refractive members 121 may include silicon nitride,and the second refractive member 122 may include silicon oxide. Thesecond refractive member 122 may cover the waveguide 111 of theresonator 110 and the Bragg gratings 120. The first refractive members121 are spaced apart from each other along the lengthwise direction ofthe resonator 110. Intervals between the first refractive members 121,that is, pitches P between the first refractive members 121, may beconstant along the lengthwise direction of the Bragg grating 120.

In the Bragg grating 120 having the above structure, materials havingdifferent refractive indexes, for example, the first refractive members121 including the silicon nitride and the second refractive member 122including silicon oxide are disposed, and the first and secondrefractive members are formed and arranged to create an interferencepattern between waves. The Bragg grating 120 having the above structuremay reflect particular wavelengths of light and have a high reflectivityat the particular wavelengths. However, the Bragg grating 120 may nothave a high reflectivity with respect to a wide wavelength band.

FIG. 4 is a graph of reflectivity of the Bragg grating 120 of FIG. 3with respect to a wavelength band of 800 nm to 900 nm. The firstrefractive members 121 and the second refractive member 122 forming theBragg grating 120 respectively include silicon nitride and siliconoxide, and pitches P between the first refractive members 121 are 290nm. Referring to FIG. 4, within a wavelength band of 800 nm to 830 nm,reflectivity is very low, that is, 20% or less. Therefore, it isdifficult to obtain high reflectivity with respect to the wavelengthband of 800 nm to 830 nm by using the Bragg grating 120 of FIG. 3. Inparticular, an ultra-small size spectroscopy device that is to beimplemented as a wearable device has to use a wavelength band having awidth of 100 nm or greater, and thus, the Bragg grating 120 having theabove described structure may not be suitable for the ultra-small sizespectroscopy device.

FIG. 5 is a plan view of a spectroscopy device according to an exemplaryembodiment.

Referring to FIG. 5, the spectroscopy device includes a plurality ofspectroscopy units 200 provided on a substrate 201. Here, the substrate201 may be, for example, a silicon substrate, but is not limitedthereto. In the exemplary embodiment, each of the spectroscopy units 200may include a Fabry-Perot interferometer, but the exemplary embodimentis not limited thereto.

Each of the spectroscopy units 200 may include a resonator 210, andBragg gratings (e.g., reflector) 220 provided at opposite ends of theresonator 210. The Bragg grating 220 provided at a first end of theresonator 210 may be connected to an input coupler 231, through whichlight is incident, and the Bragg grating 210 provided at a second end ofthe resonator 210 may be connected to an output coupler 232 throughwhich light is emitted. The first end of the resonator 210 may opposethe second end of the resonator 210.

At least some of the spectroscopy units 200 may include resonators 210having different lengths from each other. In FIG. 5, a sequence of thespectroscopy units 200 are arranged in a y-direction, and the lengths ofthe resonators 210 of the spectroscopy units 200 gradually increasealong the y-direction. The spectroscopy device having the abovestructure may be integrated on, for example, a silicon substrate, to bemanufactured as a fine chip.

FIG. 6 is a perspective view of the spectroscopy unit 200 of FIG. 5.

Referring to FIGS. 6, the spectroscopy unit 200 includes the resonator210 having a predetermined length and the Bragg gratings 220 at oppositeends of the resonator 210. The resonator 210 may include a waveguide 211including a predetermined medium for making light proceed therein. Thewaveguide 211 may have a thickness of about 100 nm to 200 nm and a widthD of about 200 nm to about 900 nm, for example. However, the exemplaryembodiment is not limited thereto, that is, the thickness and the widthof the waveguide 211 may vary. The waveguide 211 may include, forexample, silicon nitride, but is not limited thereto, that is, thewaveguide 211 may include other various materials.

FIG. 7 is an internal plan view of the Bragg grating 220 of FIG. 6.

Referring to FIG. 7, the Bragg grating 220 includes a core member 223, aplurality of first refractive members 221, and a second refractivemember 222. The core member 223 may extend from the waveguide 211 of theresonator 210 in a lengthwise direction (i.e., x-direction of FIG. 7).The core member 223 may be integrally formed with the waveguide 211 ofthe resonator 210. The core member 223 may include the same material asthat included in the waveguide 211 of the resonator 210. For example,the core member 223 may include silicon nitride, but is not limitedthereto. Otherwise, the core member 223 may include a different materialfrom that of the waveguide 211 of the resonator 210.

The first refractive members 221 may protrude from the core member 223.The first refractive members 221 may include a plurality of pairs ofarms. Each pair of arms extends outwardly from the core member 223 to bein parallel to each other and perpendicular to the core member 223. Thecore member 223 may hold the plurality of pairs of arms in fixedpositions on the core member 223. In greater detail, the firstrefractive members 221 may protrude from opposite sides of the coremember 223 in a width direction of the core member 223 (i.e.,y-direction in FIG. 7). The first refractive members 221 may be spacedapart from each other in the lengthwise direction of the core member223. Here, the first refractive members 221 may face each other acrossthe core member 223 when viewed from the top of the spectroscopy unit200, but are not limited thereto.

Intervals between the first refractive members 221, that is, pitches Pbetween the first refractive members 221, in the lengthwise direction ofthe core member 223 may be constant. The first refractive members 221may be integrally formed with the core member 223. The first refractivemembers 221 may include the same material as that of the core member223. For example, the first refractive members 221 may include siliconnitride, but are not limited thereto.

The second refractive member 222 is provided to fill spaces between thefirst refractive members 221. The second refractive member 222 mayinclude a material having a refractive index that is different fromthose of the first refractive members 221. For example, the secondrefractive member 222 may include silicon oxide, but is not limitedthereto. The second refractive member 222 may be provided to cover thewaveguide 211 of the resonator 210 and the first refractive members 221.

A width W1 of the Bragg grating 220 may be greater than the width D ofthe waveguide 211 of the resonator 210. The width W1 may be alsoreferred to as a span of the Bragg grating 220. In addition, a width W2of the core member 223 may be less than the width D of the waveguide 211of the resonator 210. Here, the width W1 of the Bragg grating 220 maycorrespond to a sum of protruding lengths L of the two first refractivemembers 221 that protrude toward opposite directions and the width W2 ofthe core member 223. In the exemplary embodiment, the width W1 of theBragg grating 220 and the width W2 of the core member 223 may beconstant along the lengthwise direction of the core member 223.Accordingly, the protruding lengths L of the first refractive members221 may be constant along the lengthwise direction of the core member223.

FIG. 8 is a graph of reflectivity of the Bragg grating 220 of FIG. 7with respect to a wavelength band of 800 nm to 900 nm. Here, the firstrefractive members 221 and the second refractive member 222 included inthe Bragg grating 220 respectively include silicon nitride and siliconoxide, and pitches P between the first refractive members 221 are 290nm. In addition, the width D of the waveguide 211, the width W1 of theBragg grating 220, and the width W2 of the core member 223 arerespectively 510 nm, 1000 nm, and 200 nm.

When comparing the graph of FIG. 4 with the graph of FIG. 8, the Bragggrating 220 of FIG. 7 may achieve higher reflectivity than the Bragggrating 120 of FIG. 3. In detail, referring to FIG. 3, the Bragg grating120 exhibits low reflectivity with respect to the wavelength band of 800nm to 830 nm. However, referring to FIG. 8, the Bragg grating 220 ofFIG. 7 exhibits high reflectivity with respect to the wavelength band of800 nm to 830 nm, as well. As described above, the Bragg grating 220according to the exemplary embodiment may achieve high reflectivity withrespect to a wider wavelength band than that of the Bragg grating 120 ofFIG. 3.

FIG. 9 is an internal plan view of a Bragg grating 320 according toanother exemplary embodiment.

Referring to FIG. 9, the Bragg grating 320 includes a core member 232, aplurality of first refractive members 321, and a second refractivemember 322. The core member 323 may extend from the waveguide 211 of theresonator 210 (see FIG. 6) in a lengthwise direction of the resonator210. The core member 323 may be integrally formed with the waveguide 211of the resonator 210. The core member 323 may include the same materialas that of the waveguide 211 of the resonator 210, but is not limitedthereto.

The first refractive members 321 may protrude from the core member 323.The first refractive members 321 may protrude from opposite sides of thecore member 323 in a width direction of the core member 323, and may bespaced apart from each other along a lengthwise direction of the coremember 323. The first refractive members 321 may be integrally formedwith the core member 323. The second refractive member 322 may beprovided to fill spaces between the first refractive members 321. Thesecond refractive member 323 may include a material having a refractiveindex that is different from that of the first refractive members 321.The second refractive member 322 may be provided to cover the waveguide211 of the resonator 210 and the first refractive devices 321.

A width W1 of the Bragg grating 320 may be greater than the width D ofthe waveguide 211 of the resonator 210. In addition, a width W2 of thecore member 323 may be less than the width D of the waveguide 211 of theresonator 210. The width W1 of the Bragg grating 320 and the width D2 ofthe core member 323 may be constant along the lengthwise direction ofthe core member 323. Therefore, protruding lengths L of the firstrefractive members 321 may be constant along the lengthwise direction ofthe core member 323.

Unlike the previous exemplary embodiment, intervals between the firstrefractive members 321, that is, pitches P between the first refractivemembers 321, may vary along the lengthwise direction of the core member323. That is, at least some of the pitches P between the firstrefractive members 321 may vary along the lengthwise direction of thecore member 323. FIG. 9 exemplarily shows a case in which the pitches Pbetween the first refractive members 321 are gradually reduced toward acenter portion of the core member 323. However, the exemplary embodimentis not limited thereto, that is, the pitches P between the firstrefractive members 321 may vary in various manners along the lengthwisedirection of the core member 323.

FIG. 10 is a graph of the reflectivity of the Bragg grating 220 of FIG.7 versus a reflectivity of the Bragg grating 320 of FIG. 9 with respectto the wavelength band of 800 nm to 900 nm. Here, a curve C1 denotes thereflectivity of the Bragg grating 220 of FIG. 7, in which the pitches Pbetween the first refractive members 221 are constant, and a curve C2denotes the reflectivity of the Bragg grating 320 of FIG. 9, in whichthe pitches P between the first refractive members 321 vary.

The first refractive members 221 and 321 and the second refractivemembers 222 and 322 in the Bragg gratings 220 and 320 respectivelyinclude silicon nitride and silicon oxide. In addition, the width D ofthe waveguide 211, the widths W1 of the Bragg gratings 220 and 320, andthe widths W2 of the core members 223 and 323 are respectively 510 nm,1000 nm, and 200 nm. In the Bragg grating 220 of FIG. 7, the pitches Pbetween the first refractive members 221 are 290 nm. In addition, in theBragg grating 320 of FIG. 9, a minimum pitch between the firstrefractive members 321 is 250 nm, and the pitch varies by 2 nm.

Referring to FIG. 10, the Bragg grating 320 of FIG. 9, in which thepitches P between the first refractive members 321 vary, exhibits highreflectivity with respect to a wider wavelength band than in the Bragggrating 220 of FIG. 7, in which the pitches P between the firstrefractive members 221 are constant. Therefore, high reflectivity may beobtained with respect to wide wavelength band by varying the pitches Pbetween the first refractive members 321.

FIG. 11 is an internal plan view of a Bragg grating 420 according toanother exemplary embodiment.

Referring to FIG. 11, the Bragg grating 420 includes a core member 423,a plurality of first refractive members 421, and a second refractivemember 422. The core member 423 may extend from the waveguide 211 of theresonator 210 (see FIG. 6) in a lengthwise direction (i.e., x-directionin FIG. 11). The core member 423 may be integrally formed with thewaveguide 211 of the resonator 210. The core member 423 may include thesame material as that of the waveguide 211 of the resonator 210. Forexample, the core member 423 may include silicon nitride, but is notlimited thereto. Otherwise, the core member 423 may include a materialdifferent from that of the waveguide 211 of the resonator 210.

The first refractive members 421 may protrude from the core member 423.Here, the first refractive members 421 may protrude from opposite sidesof the core member 423 in a width direction of the core member 423(i.e., y-direction in FIG. 11). The first refractive members 421 may bespaced apart from each other along the lengthwise direction of the coremember 423. Here, the first refractive members 421 may be arrangedfacing each other based on the core member 423, but are not limitedthereto. The first refractive members 421 may be integrally formed withthe core member 423. The first refractive members 421 may include thesame material as that of the core member 423. For example, the firstrefractive members 421 may include silicon nitride, but is not limitedthereto.

The second refractive member 422 may be provided to fill spaces betweenthe first refractive members 421. The second refractive member 422 mayinclude a material having a different refractive index from that of thefirst refractive members 421. For example, the second refractive member422 may include silicon oxide, but is not limited thereto. The secondrefractive member 422 may be provided to cover the waveguide 211 of theresonator 210 and the first refractive members 421.

The width W1 of the Bragg grating 420 may be greater than the width D ofthe waveguide 211 of the resonator 210. In addition, the width W2 of thecore member 423 may be less than the width D of the waveguide 211 of theresonator 210. Here, the width W1 of the Bragg grating 420 maycorrespond to a sum of the protruding lengths L of the two firstrefractive members 421 that protrude in opposite directions to eachother and the width W2 of the core members 423, as described above.

At least one of the width W2 of the core member 423 and the protrudinglengths L of the first refractive member 421 may vary along thelengthwise direction of the core member 423. In more detail, the widthW2 of the core member 423 may be gradually reduced from opposite endsthereof toward a center portion thereof. In addition, the width W1 ofthe Bragg grating 420 may be gradually increased from the opposite endsof the core member 423 toward the center portion of the core member 423.The width W2 of the core member 423 has a maximum value W2 _(max) at theends of the core member 423 and has a minimum value W2 _(min) at thecenter of the core member 423 in the lengthwise direction (i.e.,x-direction). The width W1 of the core member 423 has a maximum value W1_(max) at the center of the core member 423 and has a minimum value W1_(min) at the center of the core member 423 in the lengthwise direction.Accordingly, the protruding lengths L of the first refractive members421 gradually increase from the opposite ends of the core member 423toward the center portion of the core member 423.

The intervals between the first refractive members 421, that is, thepitches P between the first refractive members 421, may vary along thelengthwise direction of the core member 423. That is, at least some ofthe pitches P between the first refractive members 421 may vary alongthe lengthwise direction of the core member 423. FIG. 11 exemplarilyshows that the pitches P between the first refractive members 421 aregradually reduced toward the center portion of the core member 423.However, the exemplary embodiment is not limited to the above example,that is, the pitches P between the first refractive members 421 may varyin various manners along the lengthwise direction of the core member423.

FIG. 12 is a graph of the reflectivity of the Bragg grating 320 shown inFIG. 9 versus a reflectivity of the Bragg grating 420 of FIG. 11 withrespect to a wavelength band of 800 nm to 900 nm. Here, the curve C2denotes the reflectivity of the Bragg grating 320 of FIG. 9, and a curveC3 denotes the reflectivity of the Bragg grating 420 of FIG. 11. In FIG.12, the reflectivity is expressed in units of decibels dB.

The first refractive members 321 and 421 and the second refractivemembers 322 and 422 in the Bragg gratings 320 and 420 respectivelyinclude silicon nitride and silicon oxide. In the Bragg grating 320 ofFIG. 9, the width D of the waveguide 211, the width W1 of the Bragggrating W1, and the width W2 of the core member 323 are respectively 510nm, 1000 nm, and 200 nm. In addition, the minimum pitch between thefirst refractive members 321 is 250 nm, and the pitch varies by 2 nm. Inthe Bragg grating 420 of FIG. 11, the width D of the waveguide 211 is510 nm, and a maximum width W1 _(max) and a minimum width W1 _(min) ofthe Bragg grating 420 are respectively 1100 nm, and 670 nm. In addition,a maximum width W2 _(max) and a minimum width W2 _(min) of the coremember 423 are respectively 430 nm and 130 nm. The minimum pitch betweenthe first refractive members 421 is 250 nm, and the pitch varies by 2nm.

Referring to FIG. 12, the Bragg grating 420 of FIG. 11, in which thewidth W1 of the Bragg grating 420 varies, exhibits higher reflectivitythan the Bragg grating 320 of FIG. 9 having the constant width.Therefore, high reflectivity may be implemented by increasing the widthW1 of the Bragg grating 420 toward the center portion of the Bragggrating 420 and reducing the width W2 of the core member 423 toward thecenter portion of the Bragg grating 420.

FIG. 13 is a graph of the reflectivity of the Bragg grating 120 of FIG.3 and the Bragg grating 420 of FIG. 11 with respect to the wavelengthband of 800 nm to 900 nm. Here, a curve C denotes the reflectivity ofthe Bragg grating 120 of FIG. 3, and the curve C3 denotes thereflectivity of the Bragg grating 420 of FIG. 11. In FIG. 13, thereflectivity is expressed in the unit of decibel (dB). Referring to FIG.13, the Bragg grating 420 of FIG. 11 exhibits higher reflectivity withrespect to a wider wavelength band than in the Bragg grating 12 of FIG.4.

In the Bragg grating 420 of FIG. 11, the width of the core member 423 isgradually reduced toward the center portion of the Bragg grating 420,and the protruding lengths L of the first refractive members 421gradually increase toward the center portion of the Bragg grating 420 sothat the width W1 of the Bragg grating 420 gradually increases towardthe center portion of the Bragg grating 420. Alternatively, the width W1of the Bragg grating 420 may vary by changing the protruding lengths Lof the first refractive members 421 while maintaining the width W2 ofthe core member 423 constantly, or by changing the width W2 of the coremember 423 while maintaining the protruding lengths L of the firstrefractive members 421 constantly. In addition, the pitches P betweenthe first refractive members 421 may be constant.

As described above, when the Bragg grating includes the core member, theplurality of first refractive members protruding from the core member tobe spaced apart from each other, and the second refractive memberfilling the spaces between the first refractive members, the highreflectivity may be obtained with respect to a wavelength band of adesired width. Here, the higher reflectivity with respect to the widerwavelength band may be obtained by varying the pitches between the firstrefractive members or varying the width of the Bragg grating. Also, thematerials included in the first refractive members and the secondrefractive member may be variously selected in order to obtain higherreflectivity with respect to the visible ray band or other infrared-rayband, and the pitches between the first refractive members or the widthof the Bragg grating may be set variously. Accordingly, the spectroscopydevice that is manufactured by integrating the spectroscopy unitsincluding the above Bragg gratings on a substrate may have improvedperformance. In addition, the spectroscopy device may be manufactured asa small-sized chip that may be loaded in, for example, a non-invasiveblood glucose sensor, and may be implemented as a wearable device.

The foregoing exemplary embodiments are merely exemplary and are not tobe construed as limiting. For example, the spectroscopy unit 200 may beimplemented with any type of reflectors rather than being limited to aBragg grating.

The present teaching can be readily applied to other types ofapparatuses. Also, the description of the exemplary embodiments isintended to be illustrative, and not to limit the scope of the claims,and many alternatives, modifications, and variations will be apparent tothose skilled in the art.

What is claimed is:
 1. A Bragg grating disposed at each of opposite endsof a resonator for reflecting light of a certain wavelength band, theBragg grating comprising: a core member extending from a waveguide ofthe resonator in a lengthwise direction of the waveguide; a plurality offirst refractive members protruding from the core member; and a secondrefractive member filling spaces between the first refractive members,wherein pitches between the plurality of first refractive members varyalong the lengthwise direction, and wherein at least one of a width ofthe core member and protruding lengths of the first refractive membersvaries along the lengthwise direction.
 2. The Bragg grating of claim 1,wherein the plurality of first refractive members protrude from oppositesides of the core member in a width direction of the core member.
 3. TheBragg grating of claim 2, wherein a width of the core member graduallyreduces along the lengthwise direction of the core member toward acenter portion of the core member, and protruding lengths of theplurality of first refractive members gradually increase along thelengthwise direction toward the center portion of the core member.